Direct Volume Rendering (“DVR”) has been used in medical visualization research for a number of years. DVR can be generally described as rendering visual images directly from volume data without relying on graphic constructs of boundaries and surfaces thereby providing a fuller visualization of internal structures from 3-D data. DVR holds promise for its diagnostic potential in analyzing medical image volumes. Slice-by-slice viewing of medical data may be increasingly difficult for the large data sets now provided by imaging modalities raising issues of information and data overload and clinical feasibility with current radiology staffing levels. See, e.g., Adressing the Coming Radiology Crisis: The Society for Computer Applications in Radiology Transforming the Radiological Interpretation Process (TRIP™) Initiative, Andriole et al., at URL scarnet.net/trip/pdf/TRIP_White_Paper.pdf (November 2003). In some modalities, patient data sets can have large volumes, such as greater than 1 gigabyte, and can even commonly exceed 10's or 100's of gigabytes.
Despite its potential, DVR has not achieved widespread use for non-research medical imaging, particularly in computer network systems with visualization pipelines. This may be because DVR may need time-consuming manual adjustment using conventional transfer functions (TF) and/or editing tools. That is, the TF construction can be relatively complex and/or the tissue separation abilities may not be sufficient where dissimilar tissues have similar intensity values limiting the ability to generate diagnostic clinical renderings.